question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>The problem: A car with a mass of 1200 kg and speed 10 m/s runs into a traffic barrier at an angle of 45 degrees, and is thrown outwards at an angle of 45 degrees relative to the barrier with a speed of 5.0 m/s How big was the change in momentum of the car during the collision?</p>
<p>I tried decomposing the moment... | g10740 | [
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<p>A ladder $AB$ of mass $m$ has its ends on a smooth wall and floor (see figure). The foot of the ladder is tied by an inextensible rope of negligible mass to the base $C$ of the wall so the ladder makes an angle $\alpha$ with the floor. Using the principle of virtual work, find the magnitude of the tension in the rop... | g10741 | [
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<p>I just cooked a meat pie in the oven. Almost immediately after pulling it out of the oven, I felt that the crust was only slightly warm, but when I cut it open the filling felt very warm. I can't understand how the crust could be at a lower temperature. My understanding was that the oven heats the air, then the air ... | g10742 | [
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<p>This is a nice problem that I would like to share. </p>
<p><strong>Problem:</strong> In a public garden, there a statue consisting of a spherical stone and a stone cup. The ball is 1 meter in diameter and weighs at least a ton. The cup is an upside-down hemispherical shell, and the ball sits in this shell and fits ... | g10743 | [
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<p>Radiation is basically just particles flying around, right? Are free hydrogen atoms just typically not moving fast enough to be considered "radiation"?</p> | g10744 | [
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<p>This post is inspired by this <a href="http://math.stackexchange.com/questions/302023/best-sets-of-lecture-notes-and-articles">math.se post</a>.</p>
<p>Let me start by apologizing if there is another thread on phys.se that subsumes this.</p>
<p>I often find that I learn best from sets of lecture notes and short ar... | g10745 | [
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<p>I'm having trouble understanding the surface used for <a href="http://en.wikipedia.org/wiki/Amp%C3%A8re%27s_circuital_law" rel="nofollow">Ampere's Circuital Law</a>. In classes, we've been using simple circular or rectangular loops. Is the surface supposed to be area of the circle or the rectangle? Or is it a simple... | g10746 | [
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<p>The <a href="http://en.wikipedia.org/wiki/Random_phase_approximation" rel="nofollow">random phase approximation</a> (RPA) is an approximation method in condensed matter physics and in nuclear physics. </p>
<p>What is the difference between RPA and generalized RPA?</p> | g10747 | [
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<p>I'm doing some homework in Classical Mechanics, and is about to write out the Lagrangian of a system. But, when I check the answer from my teacher, something is missing.</p>
<p>The kinetic energy I'm using is given by:</p>
<p>$$T =\frac{1}{2}m\dot{x_{m}}^{2},$$</p>
<p>where</p>
<p>$$\dot{x_{m}} = \dot{x}+L \cos(... | g10748 | [
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<p>The Beer-Lambert law is: $ I=I_{0}e^{-n\sigma(\lambda) x} $,
where $ n $ is the volume concentration and $ \sigma $ the "efficient" cross-section.</p>
<p>For interaction with F-centers (kind of crystal defects: electrons trapped in negative ions lakes), what is the boundary effect on the exponential parameter: $ n\... | g10749 | [
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<p>It has been stated <a href="http://physics.stackexchange.com/a/100719">here</a> that:
<blockquote>we can say, without introducing a coordinate system, that the interval associated with two events is <em>timelike</em>, <em>lightlike</em>, or <em>spacelike</em></blockquote>.</p>
<p>This assertion appears at variance ... | g10750 | [
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<p>I've been reading a lot but cannot find an example of 2D Gaussian wave packet moving in a particular direction. I've done some of the math myself, in a 1D case, and then kind of guessed the generalization to 2D. I'd be thrilled if someone could confirm or correct the expression. This is supposed to model a free part... | g10751 | [
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<p>Me and my friend, both many years from learning string theory, had a recent debate about it anyway. He said he already partially discounts it because after learning waves, he believes any function, and thus any kind of physical process can be created through a superposition of an infinite sum of waves. Since string ... | g10752 | [
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<p>Well I've been asked this question, but I haven't been able to come with an answer yet using books and some web searches. The point is as the title says, to answer the question with the whole phenomenon explanation if possible. </p> | g10753 | [
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<p>I read in a book that for $\beta$-decay the electrons have always been found to have an expectation value for their helicity of $h=-v/c$. </p>
<p>Then ist is said in the book, that it follows from this fact that such electrons are in a left-handed chiral state which is characteristic for the weak interaction.</p>... | g10754 | [
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<p>I am quite interested in the understanding of the relation between p_ip wave superconductor(SC) and the Moore-Read(MR) state.</p>
<p>They share many similar properties, for example, p+ip SC has majorana as vortex excitation, MR has nonabelian quasi hole excitation. More interestingly, their wavefuncions are similar... | g10755 | [
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<p>I don't understand why there is necessarily a diffraction limitation on optical systems. Where does this limitation in focusing light come from? </p> | g10756 | [
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<p>I have an 134.2 khz RFID antenna for sport events which is basically a 1x1 meter square sheet of rubber with 3 loops of antenna cable embedded. The problem is that the transponder recognition range is drastically reduced when the ground below the antenna contains metal (e.g. reinforced concrete).</p>
<p>Would it be... | g10757 | [
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<p>I've been asking myself a question for quite some time :</p>
<ul>
<li>say that a bullet gets out of a gun at 900 km/h (I'm european, hence the metric system).</li>
<li>say a train could go in a straight line at 900 km/h</li>
<li>say you're at the back of that train, and you'd shoot a bullet backwards. The bullet ex... | g10758 | [
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<p>As can for example be learned from chapter I.2 of Anthony Zee's <em>Quantum field theory in a nutshell</em>, path integrals can be used to to calculate the amplitude for a system to transition from one state to another by considering all possible paths between the two states.</p>
<p><a href="http://motls.blogspot.c... | g10759 | [
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<p>Are there any non magnetic materials that attract to each other as if they were magnetic?</p>
<p>This is an argument I am having with a friend. </p>
<p>Thanks,</p> | g10760 | [
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<blockquote>
<p>Point A moves uniformly with velocity $v$ so that the vector $\vec{v}$ is continually "aimed" at point B which in turn moves rectilinearly and uniformly with velocity $u < v$. At the initial moment $\vec{v} \perp \vec{u}$ and the points are separated by a distance $l$. How soon will the points conv... | g10761 | [
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<p>I'm interested in the relation between the probability distribution $p_i$ over states of a system on the one side and the density of states $\rho(\eta)$ of its environment. (Meaning, $\int_{\eta_a}^{\eta_b} \rho(\eta) ~ \mathrm{d} \eta$ is the number of environment states with energies in the interval $[\eta_a, \eta... | g10762 | [
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<p>I conducted an experiment which aimed to detail and record the voltage across series resistors in series circuits.</p>
<p>I noticed that:</p>
<ul>
<li>The Final Voltage, V3, stayed the same.</li>
<li>The resistors with the highest resistance had the highest voltage drop.</li>
</ul>
<p>How do I put my observation ... | g10763 | [
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<p>I have a (hopefully) quick question: is it possible to have a null Killing field $\xi ^ \mu$ such that the twist 1-form $\omega_{\mu} = \epsilon_{\mu\nu\alpha\beta}\xi^\nu \nabla^\alpha \xi^\beta \neq 0$ but the exterior derivative $(d \omega)_{\mu\nu} = 2\nabla_{[\mu}\omega_{\nu]} = 0$? Or does $(d \omega)_{\mu\nu}... | g10764 | [
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<p>Shall we consider photoelasticity a non-mathematical, or purely visual, proof of the existence of stresses in mechanical structures undergoing external loading?</p> | g10765 | [
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<p>At a free massless Lagrangian
\begin{equation} L_0 = \frac 1 2 ( \partial \psi)^2 ,\end{equation}
add an interaction term \begin{equation} L_I = \frac 1 2 m^2 \psi^2\end{equation}
where m is small enough to converge its perturbation calculation. From these setup, is it possible to gain the same results as of the fr... | g10766 | [
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<p>Today I was doing my physics homework and there was a problem involving a space ship falling at 9.8 m/(s^2) to simulate gravity, and it asked how long would it take for the ship to reach to speed of light, and I calculated it to be just under a year. So if it takes less than a year to go to the speed of light at 9.8... | g10767 | [
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<p>Let me preface this by saying that I have a very limited knowledge of optics -- basically, I know enough to be dangerous. So I have a square Fresnel lens that measures about 10.5 inches on a side. The focal length is about 11.5 inches. I'm trying to find a presumably-smaller glass collimating lens that will take the... | g10768 | [
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<p>At the end of spontaneous symmetry breaking I get these mass terms:</p>
<p>$$W_{\mu}^{\pm}=\frac{1}{\sqrt{2}}\bigl(W_{\mu}^{1} \mp i W_{\mu}^{2} \bigr )$$</p>
<p>$$\mathcal{L}_{mass}=\frac{1}{2} g^2 \frac{v^2}{4} W_{\mu}^{+}{W^{\mu}}^{-} + \frac{1}{2} g^2 \frac{v^2}{4} W_{\mu}^{-}{W^{\mu}}^{+}$$</p>
<p>So I have ... | g10769 | [
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<p>It would really help me with an idea I have if I could see how something such as a symmetric field could collapse to something asymmetric. I know that if $x$ occures before $y$ is symmetric, then $y$ occurs before $x$, which doesn't make sense if we take time to be asymmetric (only flowing in one direction). Is the... | g10770 | [
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<p>Did the geocentric theorists also use the fact that the earth had an axis tilt? Or was their explanation of some other kind?</p> | g10771 | [
0.06564395874738693,
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0.02316960133612156,
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0.033935654908418655,
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<p>I've been considering a career change for a long time and recently discovered the Two-Slit Experiment, which, to put it frankly, blew my mind. I then started some hefty reading and investigation into all things Quantum (Bell, Campbell, entanglement, QIT), which has led me here.</p>
<p>I have 20 years experience in... | g10772 | [
0.010845396667718887,
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0.024693766608834267,
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<p>The paramount object in generalized gomplex geometry is the Courant algebroid $TM\oplus T^\star M$, where the manifold $M$ is called <em>background geometry</em> I think (I am not sure). More generally this Courant algebroid can be twisted by a closed 3-form $H$ on $M$, which I suspect is called a <em>flux</em> (I a... | g10773 | [
0.00783494208008051,
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0.005287386476993561,
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0.025178438052535057,
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0.034370310604572296,
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<p>Just what the title states.</p>
<p>Pretty much all movement on Earth is by pushing against the much greater mass of Earth. Given there are easily thousands of aircraft taking flight/landing, and a lesser number of rockets (Satellite launch etc). Understandably the effect of aircraft would be reduced because an airc... | g10774 | [
0.011766011826694012,
0.06520646065473557,
0.0012622573412954807,
0.05256453901529312,
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0.029654692858457565,
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<p>I am trying to understand why radio waves pass though the human body, light does not, but X-rays still pass. </p>
<p>In my mind I imagine that radio waves don't supply enough energy and don't excite any interesting modes of the material that they hit. This is in contrast to the photon excitation and associated scat... | g10775 | [
0.029457679018378258,
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<p>If I understand correctly, according to Einstein's General Theory of Relativity, mass results in a distortion in space-time. In turn, the motion of the mass is affected by the distortion. A result of the interplay between mass and space-time is that the 'force' of gravity may be explained away. Masses are not subjec... | g10776 | [
0.04885274916887283,
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0.05121368542313576,
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<p>Can someone summarize, with references if possible, all of the alternatives to the simplest model (that requires only a single scalar Higgs field with the Mexican Hat potential) of spontaneous electroweak symmetry breaking?</p> | g10777 | [
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0.018354063853621483,
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0.0721... |
<p>What impulse should be applied to an object of mass m, having a known coefficient of friction u to get to a distance d ?</p>
<p>Thanks!</p>
<p>Update 14.02.2011: </p>
<p>I still wasn't able to find an answer to this. Could you please share the solution? I need an "Idiot's solution" for this. I'm not experienced e... | g10778 | [
0.032172996550798416,
0.00018231973808724433,
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0.038066018372774124,
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0.06926145404577255,
0.040803976356983185,
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0.008175722323358059,
0.010958345606923103,
... |
<p>Stephen Wolfram in his book <em>A New Kind of Science</em> touches on a model of space itself based on automata theory. That it, he makes some suggestions about modelling not only the behaviour of matter through space, but the space itself in terms of state machines (a notion from computing). Here, the <a href="http... | g10779 | [
0.03356598690152168,
0.011171541176736355,
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0.0010550851002335548,
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0.002549830125644803,
0.03483487665653229,
0.026772648096084595,
0.022985383868217468,
0.... |
<p>or a phenomenon where we can only measure the standard deviation ($\sigma_w$) of a variable $w$ and not the mean $\overline{w}$</p> | g10780 | [
0.026495883241295815,
0.018982574343681335,
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0.02292441949248314,
0.025040119886398315,
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... |
<p>Is there a certain frequency of sound/noise that will cause gunpowder to explode?</p> | g10781 | [
0.02665441483259201,
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<p>I’ve been studying electricity lately and it has been quite hard to understand the terminology, and picturing it in my mind. After struggling to understand what each property of electric currents meant, I found an analogy that related electric current to water flow. I am not sure if this analogy is 100% accurate, bu... | g10782 | [
0.0641661211848259,
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0.03215741366147995,
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0.03451011702418327,
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0.04... |
<p>Almost every source I can find online maintains that two 0.5 cm blankets are significantly warmer than a single 1cm blanket due to air trapped between the thin blankets.</p>
<p>However, the thermal conductivities of air and wool are roughly comparable according to <a href="http://hyperphysics.phy-astr.gsu.edu/hbase... | g10783 | [
0.034655146300792694,
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... |
<p>The resultant force acting on a body in equilibrium is 0:</p>
<p>$$\iiint_R \rho {\bf b}\ dV + \iint_S {\bf t}^{(n)} ds = 0,$$</p>
<p>in which $R$ is a region inside the body, $\rho {\bf b}$ the body force per unit volume, $S$ the surface of the region and ${\bf t}^{(n)}$ the surface traction.</p>
<p>I am not q... | g10784 | [
0.04680892452597618,
0.043525438755750656,
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0.0232307780534029,
0.03508618474006653,
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-0.014484... |
<p>I was concerned about what determines the speed of the bullet coming out from the gun.</p>
<p>Is it determined by the strength of the explosive or how fast does it burn up?</p>
<p>For example if we take the same amount of gun powder and a plastic explosive (probably TNT) in a bullet shell which bullet will go furt... | g10785 | [
0.08153291046619415,
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0.03110024705529213,
0.029545092955231667,
0.04551165923476219,
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0.03422846645116806,
0.018444249406456947,
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0.012292961589992046,
0.035084404051303864,
-0.0... |
<p>Consider a parallel-plate capacitor. Charge is stored physically on electrodes ("plates") which are flat and parallel to one another. If one electrode has charge $+Q$ and the other electrode has charge $-Q$, and $V$ is the potential difference between the electrodes, then the capacitance $C$ is $$C = \frac{Q}{V}$$... | g10786 | [
0.06313762813806534,
0.05757075548171997,
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0.059767916798591614,
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0.023615717887878418,
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-0.05926495045423508,
0.03241189941763878,
0.007560471538454294,
-... |
<p>I would like to know how to take the functional derivative of the holonomy, or Wilson line. I have tried it and I will show what I have done below, but before I wanted to say that I also have seen and done this with the characteristic deifferential equation for the holonomy
$$
\frac{\partial U}{\partial s}+\dot{\ga... | g10787 | [
0.02311781421303749,
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0.04267707094550133,
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0.028400911018252373,
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-0.07053231447935104,
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0.039492182433605194,
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<p>I always get a little uneasy that all the theories I can think of (at least since Newton) are constructed in a way such that they would be true in heaven and on earth ... but we can never go everywhere and test it out. </p>
<p>So here is the question:</p>
<blockquote>
<p>Is there some good justification to imple... | g10788 | [
0.04167886823415756,
0.08375860005617142,
0.012235610745847225,
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0.09609446674585342,
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0.040409039705991745,
0.0... |
<p>I was reviewing the paper-<a href="http://www.sciencedirect.com/science/article/pii/S0370269304010032" rel="nofollow">Coupling of a vector gauge field to a massive tensor field</a></p>
<p>In the calculation I found the term $ 2\mu^2 \varepsilon^{ijk} \dfrac{\partial_j}{\partial^2}B_k\dot{B}$ which needed to be inte... | g10789 | [
0.04562056437134743,
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0.017914239317178726,
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0.0005612623644992709,
0.018784049898386,
-0.0... |
<p>are bubbles of spacetime pinching-off allowed solutions to general relativity? With "pinch-off bubble" i really mean a finite 3D volume of space whose 2D boundary decreases until it reaches zero and it disconnects from the mother spacetime, becoming a compact "child" spacetime</p>
<p>I've read this as a way in eter... | g10790 | [
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0.02074040099978447,
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0.029831495136022568,
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0.04428066313266754,
0.0... |
<p>Internal resistance of inductance (or other devices) are said to be in series. But <a href="http://en.wikipedia.org/wiki/Parasitic_capacitance" rel="nofollow">parasitic capacitance</a> is said to be in parallel (in case of an inductor). Why is that so? What determines whether an internal property is in series or par... | g10791 | [
0.022146614268422127,
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0.023183515295386314,
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0.003810230176895857,
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0.06192002817988396,
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<p>I recently came across <a href="http://link.springer.com/article/10.1140%2Fepja%2Fi2013-13072-1" rel="nofollow">this article</a>, published in the respectable <em>European Physical Journal A</em>. (Apparently, there isn't any corresponding arXiv article for this, so I'm sorry if everyone isn't able to access the art... | g10792 | [
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... |
<p>I am trying to wrap my head around how this would work.</p>
<p>The setup is quite simple - there are multiple flat coils sealed in insulated disks, and an active coil with alternating current underneath. All is placed in a cylinder.</p>
<p>The question is, how will the disks behave - all should induce the same mag... | g10793 | [
0.003027467057108879,
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<p>I am trying to locate peak in a data set by numerically calculating the peak using <a href="http://mathworld.wolfram.com/FunctionCentroid.html" rel="nofollow">centroid method</a>. How can I estimate the error associated with this peak determination?</p> | g10794 | [
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<p>I have a system of particles with equal distance with each other and another at random positions which is moving with time. What I want to know is :</p>
<ol>
<li><p>The method by which I can reduce the number of particles from the first system, as I know the maximum motion of any particle is X (<strong>Meaning: Max... | g10795 | [
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<p>I'm just curious what causes radioactivity. I've been told that in the case of alpha decay, since the nucleus is quantum mechanical, there is a probability that the configuration of protons and neutrons is in such a way as to have an alpha particle outside the nucleus, and then the electric repulsion pushes it away.... | g10796 | [
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0.017121... |
<p>I would like to know the following:</p>
<ol>
<li><p>What is the angle at which water gets splashed when I ride my vehicle through a water on the road?</p></li>
<li><p>How does angle of water varies with speed?</p></li>
<li><p>What is the relation between the distance the water goes with the speed of the vehicle?</p... | g10797 | [
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0.03362959250807762,
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0.028669720515608788,
0.035024553537368774,
0.0... |
<p>I know the hypothesis that the light speed is constant is retained by experiments. But is there any theory explaining why the light speed is constant no matter how an observer moves relative to light?</p>
<p>My question is, specifically: Suppose an observer $O$ launches a light and $O$ starts to move at the same ti... | g348 | [
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0.0... |
<p>Given the lowest eigenvalue $E_0$ of an Schrödinguer operator, do the other energies $ E_{n} $ for $ n >0 $ depend strongly on the lowest eigenvalue of the system? I mean, if we somehow fixed the eigenvalue $E_{0}$, could we get more or at least better approximations to the other eigenenergies of the system?</p>
... | g10798 | [
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<p>It is postulated by many cosmologists that at the Big Bang time the universe was in an unusual low entropy state.</p>
<p>Does this claim specifically mean that the entropy of the initial universe was zero?</p>
<p>Is zero-entropy state unique for given physical laws?</p>
<p>Is it possible that entropy was growing ... | g10799 | [
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<p>Let's have minimally extended gauge invariant lagrangian (with free kinetic term of EM field):
$$
\tag 1 L (\Psi , \partial_{\mu} \Psi) \to L (\Psi , D_{\mu}\Psi ) - \frac{1}{4}F^{\mu \nu}F_{\mu \nu}, \quad D_{\mu} = \partial_{\mu} - iQA_{\mu}.
$$
Here $A_{\mu}$ is given by $F_{\mu \nu} = \partial_{\mu}A_{\nu} - \pa... | g10800 | [
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0.02... |
<p>In Peskin and Schroeder p. 669 it is argued that the axial current can be parametrized between the vacuum and an on-shell pion state as:</p>
<p>$$<0|j^{\mu 5}(x)|\pi^b(p)>=-ip^\mu f_\pi \delta^{ab}e^{-ipx}$$</p>
<p>This is then described as a parametrization of the amplitude for the axial current to create a... | g10801 | [
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<p>I am trying to understand what a term like $$ \mathcal{L}_{int} = (\partial^{\mu}A )^2 B^2 $$ with $A$ and $B$ being scalar fields for instance means. I understand how to draw an interaction term in Feynman diagrams without the derivative and how to interpret it (connecting external lines, find the correct value for... | g10802 | [
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<p>I am learning about waves (intro course) and as I was studying Wave Functions, I got a little confused.</p>
<p>The book claims that the wave function of a sinusoidal wave moving in the $+x$ direction is $y(x,t) = A\cos(kx - wt)$.</p>
<p>However, I see a drawing of the wave and they always seem to be $\cos$ graphs.... | g10803 | [
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<p>I'm convinced that radians are, at the very least, the most convenient unit for angles in mathematics and physics. In addition to this I <em>suspect</em> that they are the most fundamentally natural unit for angles. What I want to know is why this is so (or why not).</p>
<p>I understand that using radians is useful... | g10804 | [
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<p>I know it's not possible with Earth today, but With today's level of material science technology, would it be possible to make cable strong and light enough to make a space elevator system connecting a Mars-synchronous satellite to an anchor on Mars' surface, ignoring any load at all by an elevator car? Or can someo... | g10805 | [
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<p>I am wondering if someone could provide me with a formula that would tell me at what velocity a projectile can be launched from something using an electromagnetic field. The idea is much like a rail gun or Gauss rifle, but not exactly.</p>
<p>Just looking to find a formula to determine the speed of the projectile.<... | g10806 | [
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<p>When we pierce a balloon with a sharp needle, it pops and produce a great sound. But, It doesn't pop when we open the mouth of the balloon (through which we have blown air)...</p>
<p>So, Why doesn't the gas release slowly when we pierce it with a needle. In fact, it is released slowly when we release the mouth. </p... | g10807 | [
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<p>I have an electron moving with speed $u'$ in a frame $S'$ moving with speed $v'$ relative to a rest frame $S$.</p>
<p>How do I find the total energy and momentum of the electron in the rest frame $S$?</p>
<p>I thought the equations were:</p>
<p>$E_{total} = \gamma \times mc^2$<br>
$p = \gamma \times mv$</p>
<p>B... | g10808 | [
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<p>Is the S-matrix the only observable in string theory? What about time varying spacetime backgrounds, or thermal states then?</p> | g10809 | [
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<p>A theoretical question which thought about instead of writing my C++ code. I know it is poorly defined however I am now intrigued as to the answer!</p>
<p>If you got into a boat in the middle of the sea before sunrise, and as the sun cam up sailed directly towards it, and continued to do so throughout the day until... | g10810 | [
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<p>Norton's dome is the curve $$h(r) = -\frac{2}{3g} r ^{3/2}.$$ Where $h$ is the height and $r$ is radial arc distance along the dome. The top of the dome is at $h = 0$. </p>
<p><img src="http://i.stack.imgur.com/t7JI7.gif" alt=" "></p>
<p><em>Via <a href="http://www.pitt.edu/~jdnorton/Goodies/Dome/index.html">Norto... | g10811 | [
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<p>Proca action/equation describes massive spin-1 particle, but I was unable to find an equation that describes massless spin-1 particle. </p>
<p>Can anyone tell me what the name of this equation is?</p> | g10812 | [
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<p>Let a person of mass ( m ) = 10kg. then his weight will be 98N. Now, when he jumps from 1m height on the ground, the impact force becomes 9800N ( considering deflection of ground after impact is 1cm ). 100 times. But i am highly confused. 100 times force should simply crush a human! how the force is neutralized?</p>... | g10813 | [
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<p>What is the <a href="http://en.wikipedia.org/wiki/Pseudotensor" rel="nofollow">pseudo tensor</a> in relativity?
How do we transform tensor and pseudo tensor under parity?</p> | g10814 | [
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<p>Suppose I have an empty room of $24 m^3$ and I want to heat it to 50 °C, assuming the current room is well isolated and the current temperature is 20 °C. </p>
<ul>
<li>How much power (in Watts) would a single heating element need to produce in order to reach the 50°C? </li>
</ul>
<p>Having googled around I found t... | g10815 | [
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<p>we know that for a one component system</p>
<p>$$U= TS - PV + N \mu$$</p>
<p>Now all terms on the right hand side have well defined zeros, but the internal energy is known to be a relative quantity, with no unique zero. What's going on?</p>
<p>Similarly, we derive the above from the fact that:</p>
<p>$$U(kS, kV,... | g10816 | [
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<blockquote>
<p>A uniform rod is 2.0 m long. The rod is pivoted about a horizontal, frictionless pin through one end. The rod is released from rest at an angle of 30° above the horizontal. What is the angular acceleration of the rod at the instant it is released?</p>
</blockquote>
<p>I just used </p>
<p>$$sin(30) =... | g10817 | [
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<p>A BWR reactor core may contain up to 146 tons of uranium. Why does it not form a critical mass when molten? Are there any estimates of the critical mass of the resulting zirconium alloy, steel, concrete and uranium oxide mixture?</p> | g10818 | [
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<p>The reply to a question about <a href="http://physics.stackexchange.com/questions/7131/origin-of-elements-heavier-than-iron-fe">nucleosynthesis</a>, that heavier than iron elements are produced in supernovae explosions, raised for me the following question which I could not answer by googling. Partially because the ... | g10819 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/6400/are-tidal-power-plants-slowing-down-earths-rotation">Are tidal power plants slowing down Earth's rotation?</a> </p>
</blockquote>
<p>Since we have various energy acquiring facilities that harves... | g349 | [
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<p>I don't really know anything about physics even though I pretended studying it for years.</p>
<p>How is this explained?: <a href="http://andrewsullivan.theatlantic.com/the_daily_dish/2011/01/if-you-think-youre-cold-.html" rel="nofollow">http://andrewsullivan.theatlantic.com/the_daily_dish/2011/01/if-you-think-youre... | g10820 | [
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<p>I was reading an article in this months issue of Physics World magazine on the three main theories of extra dimensions and stumbled across something I didn't quite understand when the author began talking about detecting particles in extra dimensions at a particle lab, such as the LHC in Geneva, Switzerland.</p>
<p... | g10821 | [
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<p>While studying quantum mechanics from standard textbooks I always felt some conceptual gap that was never mentioned or explained. In what follow I tried to formulate my question, please be patient with me.</p>
<p>For a quantum particle in an infinite potential well the stationary states are labelled by the quantum ... | g10822 | [
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<p>Why different objects have different colour? When a white light (composed of all colour) falls on a red book, is it true that only red colour is reflected back? If no, then why it appears red. If yes, then why does the book doesn't get warmer even if it absorbed rest other wavelengths. How is hot red iron rod differ... | g10823 | [
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<p>It has been claimed (e.g. <a href="http://physics.stackexchange.com/a/36178/10552">here</a>) and apparently already been established, that the interval $x - y$ being (called) "spacelike" implies that $\bigl[\hat O (x),\, \hat O' (y)\bigr]=0$ for any two (not necessarily distinct) operators $\hat O$ and $\hat O'$ cor... | g10824 | [
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<p>In a scanning electron microscopy, secondary electrons are defined as the electrons which obey inelastic scattering whereas backscattering electron follow elastic scattering. </p>
<p>Now my question </p>
<blockquote>
<p>Can backscatter electrons produce same level of solution as secondary electrons? </p>
</bloc... | g10825 | [
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<p>I think I have learned in physics that escape velocity is defined as the speed at which objects going ballistic in the opposite direction of the main gravitational force are able to finally overcome that force (assuming the simplest case with two directly opposing forces).</p>
<p>This means objects ballistically mo... | g10826 | [
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<p>My understanding of weak gravitational lensing is that it assumes random alignment distribution of galaxies in order to estimate statistical shear and convergences, which are used to estimate matter distributions. This might be subject to noise that depends on the granularity and presence of galaxies, and the expect... | g10827 | [
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<p>I have always pictured <a href="http://en.wikipedia.org/wiki/Volume_element" rel="nofollow">volume element</a> as a small cuboid in with volume $dx dy dz$. however in <a href="http://en.wikipedia.org/wiki/Curvilinear_coordinates" rel="nofollow">curvilinear system</a>, how would the shape of this volume element be?</... | g10828 | [
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<p>Is there a difference in <a href="http://en.wikipedia.org/wiki/Binet_equation" rel="nofollow">Binet's equation</a> when the force acting on a body is attractive and repulsive? </p>
<p>I mean, if the force has a magnitude $F(r)$, is it Binet's equation always $$\frac{d^2u}{d\theta ^2}+u=-\frac{F(u^{-1})}{mh^2u^2}, u... | g10829 | [
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<p>Can the vacuum be understood as a physical/chemical/material substance? </p>
<p>Remark: Vacuum has a density energy (so it has a density "mass" equivalence due to $E=mc^2$). Vacuum is quantum (but not classically!) polarizable (vacuum polarization effects are essential in QED or QCD).</p>
<p>Remark (II): A chemica... | g10830 | [
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... |
<p>How to prove that if a particle performs cyclical motion then its energy loss rate averaged over the period equals averaged radiation intensity?</p>
<p>The energy loss rate is the quantity of energy that the particle loses in unit time. And radiation intensity is an energy which observer detects some time later tha... | g10831 | [
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<p>Well, the difference between the two expressions $\langle \hat p^2 \rangle_{\psi}$ and $\langle \hat p \rangle_{\psi}^2$ is exactly $\Delta p^2$ , i.e. the squared uncertainty (variance) of the momentum,
where the $\hat p$ is momentum operator and uncertainty on the momentum operator is defined by:
$$\Delta p= \sqr... | g10832 | [
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<p>I've recently been working through a lot of physics problems and a lot of them say to assume that the mass of the string used in a problem involving a pulley, for example, is negligible. Why is this important? What would happen if the mass of the string wasn't negligible? </p> | g10833 | [
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<p>A container filled with fluid is accelerating initially with a1 and instantly changes to a2 (a2 < a1). What would happen to the fluid in the container. </p>
<p>My thoughts on this - If the velocity of the system is v1 when the acceleration changes to a2.
The fluid will, at that instant, have a velocity of v1 whi... | g10834 | [
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<p>I wonder if someone can help me with the following problem.</p>
<p>I send a light beam to a distant galaxy which then bounces back to me.</p>
<p>I measure the travel time of the lightbeam using say a light clock of fixed size which I assume measures conformal time $\tau=\int dt/a(t)$.</p>
<p>Is the proper distanc... | g10835 | [
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<p>I was playing with some High-Voltage the other day, when a question popped into my head. Can you calculate length of an electrical arc? It probably would be proportional to :-<br>
1. Voltage of the source<br>
2. Spark gap<br>
3. Relative Humidity (in air only)<br>
4. Resistivity of Medium<br>
5. Shape of the Electro... | g10836 | [
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<p>This photo was published at <a href="http://www.stern.de/bdt/bilder-des-tages-gefaehrliche-tropfen-1501450-4a50503e928f997c.html" rel="nofollow">stern magazine online</a>.
<img src="http://i.stack.imgur.com/Ryhyi.jpg" alt="contaminated water leaks out of vessel"></p>
<p>I wonder which information about the physical... | g10837 | [
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